The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
Free tracker included with every download this week
BMI Calculator by Age — Understanding Your Results
BMI (Body Mass Index) is a useful health screening tool that works the same way regardless of age, but interpreting your results does depend on whether you're an adult or child. Our free BMI calculator helps you find your BMI instantly using your height and weight in UK measurements. Understanding where your BMI falls within NHS categories is the first step towards managing your weight and health — and it's the same healthy bmi uk guidelines that your GP uses when assessing your health risk.
10,000+ calculations today · NHS-aligned thresholds · 100% free
Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
How to Use the BMI Calculator on This Page
The BMI calculator above is simple to use. Enter your height in centimetres or feet and inches, your current weight in kilograms, stone, or pounds, and your age, then click calculate. The tool instantly shows you your BMI number and tells you which NHS category you fall into.
Your BMI result represents your weight relative to your height. The bmi formula used is: weight (kg) ÷ height (m)². You don't need to calculate this manually — the calculator does it for you. Once you have your number, compare it against the NHS bmi categories below.
- Under 18.5: Underweight
- 18.5–24.9: Healthy weight
- 25–29.9: Overweight
- 30–34.9: Obese (Class I)
- 35 and above: Obese (Class II/III)
Remember, BMI doesn't distinguish between muscle and fat, so athletes or very muscular individuals may have a higher BMI despite being healthy. Use the weight converter on this page if you need to switch between kg, stone, and pounds.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
What Your BMI Result Means for Your Health
Your BMI number tells you how your weight relates to your height, but what is a healthy bmi can vary slightly depending on your ethnicity. For most UK adults, a healthy bmi range is 18.5 to 24.9. However, if you're of South Asian, Chinese, Black African, or Black Caribbean heritage, the NHS recommends a lower healthy range of 18.5 to 22.9 — because these groups face higher health risks at the same BMI levels.
If your BMI is in the overweight bmi or obese range, it doesn't mean you're unhealthy — but it does suggest speaking with your GP about lifestyle changes or health checks. Even losing 5–10% of your body weight can reduce your risk of type 2 diabetes, high blood pressure, and heart disease. Your GP can offer personalised advice based on your age, health history, and individual circumstances.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Does BMI change with age?
BMI is calculated the same way at any age, but how it's interpreted changes. BMI categories for adults (18+) are fixed. For children under 18, different age-specific charts apply because children's bodies change as they grow. If you're calculating BMI for a child, use the NHS Healthy Weight Calculator instead.
What should my BMI be at my age?
Healthy BMI targets are the same across all adult ages: 18.5 to 24.9 for most adults, or 18.5 to 22.9 for South Asian, Chinese, Black African, and Black Caribbean adults. Age doesn't change the target — though your GP may consider age-related health factors when giving personalised advice.
Is BMI accurate for older adults?
BMI is less accurate for people over 65 because muscle mass naturally decreases with age, which can inflate BMI readings. Your GP can assess your overall health using other measures like waist circumference and blood pressure, not just BMI alone.
What should I do if my BMI is high?
If your BMI is in the overweight or obese range, speak with your GP. They can discuss lifestyle changes like diet and exercise, check for weight-related health conditions, or refer you to specialist weight management services. Even modest weight loss improves health outcomes.
Can I use this calculator if I'm pregnant?
BMI is less reliable during pregnancy because you're expected to gain weight. Instead, speak with your midwife or GP about healthy weight gain during pregnancy. They'll give you personalised guidance based on your pre-pregnancy BMI and individual circumstances.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.